The invention relates to a method for the automatic or semiautomatic distance measurement and focusing of the image of an object onto a focal plane, whereby the image is obtained via a lens which is movable in the direction of its optical axis to effect a focus.
An arrangement for the automatic focusing with the assistance of photodiodes and an electronic circuit is known from the periodical Electronics (Nov. 10, 1977, pages 40 ff). The known arrangement functions according to the method of angular measuring, whereby two separate images of the object are projected onto two surface-like arrangements of photodiodes with the assistance of mirrors. With the assistance of a small motor, the lens and one of the mirrors is moved until the mean brightness of photodiodes corresponding to one another coincides. This method functions with an analog processing circuit such as can be realized in the technology of bipolar integrated circuits.
A difficulty of the known method is that, in principle, it requires large silicon surfaces for the integration. This can only be realized with relatively high outlay since an expensive bipolar analog technology is required.